#include<iostream>
#include<algorithm>

using namespace std;

typedef long long LL;

const int N = 1e6 + 10;

int primes[N], cnt;
int phi[N];
bool st[N];

LL get_eulers(int n)
{
	phi[1] = 1;
	for (int i = 2; i <= n; i++)
	{
		if(!st[i])
		{
			primes[cnt++] = i;
			phi[i] = i - 1;
		}
		for (int j = 0; primes[j] <= n / i; j++)
		{
			st[primes[j] * i] = true;
			if (i % primes[j] == 0)
			{
				phi[primes[j] * i] = phi[i] * primes[j];
				break;
			}
			phi[primes[j] * i] = phi[i] * (primes[j] - 1);
		}
	}

	LL res = 0;
	for (int i = 1; i <= n; i++) res += phi[i];
	return res;
}

int main()
{
	int n;
	cin >> n;

	cout << get_eulers(n) << endl;

	return 0;
}